There is a strong and growing interest in the use of hydrogen as a next generation fuel. The main reason for this interest is that hydrogen is a very clean and non-polluting fuel which, when reacted with oxygen, gives off water as its only byproduct. Although elemental hydrogen does not naturally exist on the surface of the earth, it can be produced from a number of abundant materials such as water.
The generalized, widespread use of hydrogen as a fuel presents significant challenges primarily related to development of practical hydrogen storage methods and/or materials. For example, in the gaseous state, hydrogen is volumetrically impractical. Compressing or liquefying hydrogen as storage options is energetically impractical and highly pressurized tanks of a flammable gas mandate substantial safety considerations.
For these reasons, there has been much effort in making and studying materials which store hydrogen, e.g., solid hydride materials. For commercial viability, such solid hydride materials are preferably capable of storing at least 4.5% of hydrogen by weight.
Some hydride materials, such as magnesium hydride and aluminum hydride-based materials, have hydrogen storage capacities exceeding 4.5% by weight. However, prior to the innovations embodied in the present invention, such hydride materials have significant limitations in their commercial use. One of the greatest limitations has been that these materials are capable of releasing hydrogen only at temperatures exceeding 100° C. These high operating temperatures require inputs of energy which cause them to be of limited practical utility.
Accordingly, there has been an ongoing effort to find hydride materials which are capable of controllably releasing hydrogen without requiring substantial inputs of heat. For example, it would be highly advantageous for a hydrogen storage material having a high hydrogen content to controllably release hydrogen at temperatures at or below 100° C. Such lower temperatures are particularly advantageous since these temperatures are within some of the operating temperatures of proton exchange membrane (PEM) fuel cells, internal combustion engines, and similar devices.
It is known that alanes (e.g., aluminum hydride, AlH3) and the complex aluminum hydrides (alanates such as LiAlH4 and NaAlH4) can be stimulated to desorb hydrogen at lower temperatures by processing in the presence of a metal catalyst (also referred to as dopants). The metal catalysts are typically transition metal-based materials. Among the most popular metal catalysts are those based on titanium, iron, cobalt, and nickel. The catalyst can be in the elemental form, or in the form of metal salts, such as TiCl3, TiCl4, Ti(O-n-C4H9)4, Fe(OC2H5)2, Al3Ti, and the like. See, for example, U.S. Patent Application Publication No. 2004/0247521 A1 to Bogdanovic, et al., and U.S. Pat. No. 6,773,692 B2 to Pecharsky et al., the entire contents of which are incorporated herein by reference.
In Pecharsky, et al., hydrogen is extracted from solid hydrides during mechanical processing, preferably in the presence of stoichiometric and catalytic amounts of such transition metal catalysts, while Bogdanovic, et al. claim alkali metal alanate hydrogen storage materials that have been “doped” with such metal catalysts that are nanoparticulate, finely divided or have large specific surface areas.
There remains a need for practical hydrogen storage hydride compositions for low temperature production of hydrogen which do not require either simultaneous processing in the presence or absence of such metal catalysts or other dopants and/or which are not alkali metal alanates doped with such metal catalysts. The present invention relates to such compositions and uses thereof for the production of hydrogen.